Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Stock-Based Compensation [Abstract]

Components of Stock-Based Compensation Expense

Following is the stock-based compensation expense related to common stock options, restricted common stock, common stock warrants and deferred stock units:

	Year Ended December 31,
	2022		2021
Research and development	$	810	$	420
General and administrative		2,057		1,656
Total stock-based compensation expense	$	2,867	$	2,076

Weighted Average Assumptions Used to Determine Fair Value of Options Granted

The fair value of the options granted is determined using the Black-Scholes option-pricing model. The following weighted average assumptions were used:

	2022			2021
Risk-free interest rate		1.85	%		0.66	%
Expected life of the options	5.7 years			6.0 years
Expected volatility of the underlying stock		93.7	%		91.7	%
Expected dividend rate		0	%		0	%

Stock Option Activity

The following table summarizes the stock option activity in the stock-based compensation plans:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2020		3,987,575		$	4.29
Granted		2,660,000			2.39
Forfeited/Cancelled		(1,603,073	)		5.31
Exercised		(148,941	)		2.35
Outstanding, December 31, 2021		4,895,561		$	3.14
Granted		1,070,000			1.75
Forfeited/Cancelled		(220,000	)		2.68
Exercised		—			—
Outstanding, December 31, 2022		5,745,561		$	2.90		7.38	$	30
Exercisable, December 31, 2022		3,551,395		$	3.35		6.71	$	29

Outstanding and Exercisable Options under Stock Based Compensation Plans

The following table summarizes additional information regarding outstanding and exercisable options under our stock-based compensation plans at December 31, 2022:

	Options Outstanding						Options Exercisable
Exercise Price (Range)	Number of Shares		Weighted Average Remaining Contractual Life		Weighted Average Exercise Price		Number of Shares		Weighted Average Exercise Price
			(in years)
$0.87 – 1.00		120,500		3.96	$	0.89		120,500	$	0.89
$1.01 – 3.00		4,364,521		8.11		2.19		2,300,356		2.31
$3.01 – 5.00		903,040		5.85		4.14		773,039		4.31
$5.01 – 8.00		220,000		5.11		5.92		220,000		5.92
$8.01 – 13.38		137,500		1.06		13.38		137,500		13.38
		5,745,561		7.38	$	2.90		3,551,395	$	3.35